Abstract
Stick to its technology development roadmap towards HEV industrialization, GAC Engineering has developed a E4WD (electric 4 wheel drive) hybrid electric vehicle, where an ISG motor is integrated between the engine and transmission and propels the front wheels together with the engine through an AMT, and a ERAD (electric rear axle drive) motor propels the rear wheels through a reduction gear. Comparing to other full hybrid of the same configuration (and hence the same number of motors), this concept has an additional 4WD function which adds more value for customers. This paper presents a control strategy for this configuration which will improve not only fuel economy but also drive comfort. For the ease of our description, the concept of OHPE (Overall HEV Powertrain Efficiency) and virtual pedal are introduced. By OHPE we consider not only the efficiency of engine, but also that of electric motors, power battery, and transmission. While the real acceleration pedal represents the torque demand of the whole vehicle, the virtual pedal reflects the real torque demand of the front axle and hence serves more proper for gear selection based on AMT gear shifting look-up table. Our control strategy is based on the optimization of OHPE which, under the constraint of meeting the torque demand for a given pedal position at certain vehicle speed, evaluates the overall HEV powertrain efficiency for every possible set of torque split and gear selection and picks up the best as the control target. In addition, the regeneration braking strategy and gear shift assist strategy using ERAD motor are also developed for this E4WD HEV. The NEDC cycle test and several road tests in Guangzhou have shown significant improvement of both fuel economy and the drive comfort.
KEYWORDS – HEV, E4WD, torque split, ERAD, shift assist, virtual pedal